Corticosteroid-induced chromatin loop dynamics at the FKBP5 gene

FKBP5 is a long glucocorticoid-inducible gene implicated in psychiatric disorders. To investigate the complexities of chromatin interaction frequencies at the FKBP5 topologically associated domain (TAD), we deployed fifteen one-to-all chromatin capture viewpoints near gene promoters, enhancers, introns, and CTCF-loop anchors. This revealed a 'one-TAD-one-gene' structure encompassing the FKBP5 promoter and its enhancers. The FKBP5 promoter and its two glucocorticoid-stimulated enhancers roam the entire TAD while displaying subtle cell type-specific interactomes. The FKBP5 TAD consists of two nested CTCF loops that are coordinated by one CTCF site beyond the FKBP5 polyadenylation site and another in its 8th intron, 61 kb further. Loop extension correlates with transcription increases through the intronic CTCF site. This is efficiently compensated for, since the short loop is restored even under high transcription regimes. The boundaries of the FKBP5 TAD consist of divergent CTCF sites, harbor multiple smaller genes and are resilient to glucocorticoid stimulation. Interestingly, both FKBP5 TAD boundaries harbor H3K27me3-marked heterochromatin blocks that may reinforce them. We propose that cis-acting genetic and epigenetic polymorphisms underlying FKBP5 expression variation are likely to reside within a 240 kb region that consists of the FKBP5 TAD, its left sub-TAD, and both its boundaries. Overall design: The cells were cultured in the presence of 100 nM triamcinolone acetonide(TA). Cells were then collected for 4C-seq.